Suitable fixing systems are usually used for locking workpieces to be machined on a machine tool.
A particular type of fixing systems consists of a clamp which, by means of an oil hydraulic drive, is movable both in a rotating manner about an axis of rotation and in a sliding manner along the same axis of rotation.
The clamp is mounted overhanging on the rod of an oil hydraulic actuator partly inserted in an oil hydraulic cylinder.
Between the rod and the oil hydraulic cylinder there are roto-translation means, i.e. special constraint means that allow the rod, and therefore the clamp mounted on it, roto-translating.
Such fixing systems must be able to exert huge locking forces on the piece being machined.
This need is particularly felt, e.g., in the automotive sector, in which the continuous need to optimize production cycles has led to the use of tools that operate at very high speeds, discharging on the workpiece huge forces and vibrations which must be compensated by the fixing systems.
Still in the automotive sector, moreover, the use is increasingly more frequent of particularly lightweight materials such as aluminum which, nevertheless, during the machining on the machine tool, are not able to ensure the same resistance as materials such as cast iron and steel.
It is therefore necessary that the locking clamp of the workpiece, besides exercising a very high force, rests on the workpiece at predetermined points, with great precision and in a repeatable way each time a new workpiece to be machined is mounted on the machine tool; on the contrary, in fact, the high force exerted by the clamp may cause the deformation of the workpieces, which compromises the quality of the machining and the risk of getting out-of-tolerance workpieces.
In this regard the fact should also be underlined that the high forces that the clamp exerts on the workpiece lead the rod to bend and/or twist, which not only risks damaging the oil hydraulic cylinder but changes the contact area between the clamp and the workpiece, thus increasing the risk of performing faulty machining operations.
Each fixing system by roto-translating clamp is therefore characterized by its own operating curves, which put the oil pressure inside the oil hydraulic cylinder in relation with the actual locking force exerted by the clamp and with the maximum length of the clamp, i.e., with the maximum permitted overhang.
Clearly, the pressure/force curve has an increasing pattern while the pressure/length curve has a decreasing pattern and the fixing systems of known type must work in situations of compromise which are not always entirely satisfactory.
In the light of what has been said it is easy to understand that the fixing systems by roto-translating clamp are susceptible to improvements.